Improved pharmacotherapies for the opioid addiction treatment are needed to maintain addicts in treatment for extended periods. Development of a novel drug delivery system will also keep the addicts away from high-risk tuberculosis and HIV/AIDS transmission associated with the intravenous drug abuse. One of the current treatments for opioid addiction is to use opioid agonists and/or antagonists, which generally have chemical structures similar to those of opioid. One such opioid substitution agent on the treatment horizon is structures similar to those of opioid. One such opioid substitution agent on the treatment horizon is buprenorphine. Currently, sublingual administration of buprenorphine is an investigational pharmacotherapy for the treatment of opioid addiction. However, a sustained release preparation of buprenorphine will have an advantage over current dosage forms, which require dosing daily or three times a week. Thus, the development of a novel drug delivery system of buprenorphine capable of maintaining a therapeutically useful plasma concentration over an extended period is recognized as an important area of research. In order to delivery buprenorphine at a constant rate over a prolonged period, we proposed to develop biodegradable implant systems. These implant systems will include i) biodegradable microcapsules, and ii) in situ polymeric gel. These implant systems will be developed using several grades of poly(lactide-co-glycolide) and poly(caprolactone). The first delivery system, sustained release microcapsules, will be prepared by a novel biodegradable polymers in a water miscible biocompatible solvent, e.g., N-methyl-2- pyrrolidone, dimethyl sulfoxide, ethyl acetate, acetone, ethanol, and propylene glycol. This polymer solution containing buprenorphine will be injected into the body. The water miscible solvent will diffuse from the site of infection and water will permeate into the polymer matrix resulting in a solid implant. Buprenorphine, encapsulated into polymer matrix, will release slowly over an extended period. Following the preparation, these delivery systems will be evaluated for physicochemical characteristics. These preparations will be tested in rats for preclinical evaluations, which include pharmacokinetic studies and biological compatibility studies, Following the successful preclinical evaluations, these novel delivery systems can be used, in the future, for clinical trials. Thus, the development of these novel delivery systems will bring a new pharmacotherapy for opioid addiction treatment.